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Lateral spinothalamic tract pathway

Pain and Temperature Pathways

(Lateral Spinothalamic Tract)

Receptors

The sensory pathways that deliver pain and temperature information to the brain are each composed of a receptor and three successive neurons.

A receptor is the initial portion of the first neuron in a pathway, which is sensitive to changes in the environment (= stimuli). Pain receptors (nociceptors) and temperature receptors (thermoreceptors) are unencapsulated and branched, like the fine roots of a plant.

Because nociceptors and thermoreceptors contain no specialized structures, they are often referred to as free nerve endings. They are especially abundant in the skin but occur elsewhere in the body. Internal nociceptors are found in a variety of organs, such as the muscles, joints, bladder, gut, and digestive tract.

Neurons and Pathway

The first neuron in a pain or temperature pathway is called a sensory neuron (or first-order neuron). An axon of a sensory neuron passes through the dorsal root ganglion and extends to the dorsal horn of the spinal cord, where it synapses with a second-order neuron (or interneuron). The term interneuron applies to any neuron within the central nervous system.

First-order neuron, second-order neuron, and spinal cord

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The axon from the second-order neuron decussates (crosses) within the spinal cord and ascends in the lateral spinothalamic tract, along with other second-order neurons.

Lateral spinothalamic tract and second-order neuron

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The spinothalamic tract axons pass through the medulla oblongata region of the brain before terminating at the thalamus’s ventral posterolateral (VPL) nucleus.

Full pain and temperature pathway, showing lateral spinothalamic tract, medulla oblongata, and brain

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In the thalamus, the second-order neuron synapses with a third-order neuron (interneuron). The axon of the third-order neuron then carries signals to the primary somatosensory region of the cerebral cortex, where the input is imaged and interpreted.

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References and Attributions

OpenStax, Anatomy and Physiology – “Central Processing.”

Access for free athttps://openstax.org/books/anatomy-and-physiology/pages/1-introduction


Wikipedia – “Spinothalamic Tract.”